This invention relates to web winding machines, and, in particular, to a surface winder in which a core and the product wound on the core is held against the winding rollers by vacuum.
In the field of winding and reeling, there are two basic and well-known methods for winding a web or strip of material on cores, namely, center winding and surface winding. In center winding, a core is mounted on a driven mandrel, or driven mandrels are inserted into one or both ends of a core. The mandrel rotates the core to wind the web on a core. An automatic winder which includes multiple mandrels mounted on a rotating turret which indexes from one position to the next is described in U.S. Pat. No. 2,611,552. For higher speed continuous operation, a continuously rotating turret can be used as described in U.S. Pat. No. 2,769,600.
In a center winding machine, the rotating speed of the mandrel must decrease as roll build-up occurs. U.S. Pat. No. 2,995,314 describes a means for achieving a controlled rate of deceleration as a function of the rate of roll build-up either mechanically or electrically.
Current state of the art for center winding includes continuously rotating turrets and variable speed mandrel drives to achieve speeds over 2500 feet per minute. Because the mandrel is driven at a controlled rate, and because there are no external rollers, belts, or other devices which contact the outer surface of the roll being wound, center winding has distinct advantages relative to high loft or highly embossed sheets since it does not apply excessive external pressures which calender the sheet or compress the embossments.
However, the steps of mounting the cores on the mandrels and stripping the completed logs from the mandrels are time-consuming and can limit the productive ratings for high speed machinery. This is especially true when rolls of relatively short length are being wound which must be stripped from the mandrel more frequently. It will be recognized that as machines get wider, more time is required for stripping the wound product or log, and this, too, can be speed-limiting. The small diameter mandrels can also experience vibration as they rotate at high speed, thereby imposing a limit on machine speed. There are also practical limits to the length of the mandrel relative to an acceptable core diameter, the core diameter being dictated by marketing considerations and dispensing means. Limits on the width of center winding machines affect the production rate.
The second well-known method of winding is surface winding in which the core and/or material being wound thereon are driven by contact with belts, rotating rolls, or the like which rotate at or near web speed. Again, this field is replete with numerous examples of surface winding devices.
Narrow webs can be wound on cores that are trapped within a three-roll system, or which are driven from one or both ends. When web widths exceed about 40 inches, caging or entrapment means are needed to keep the wide core and wide roll in contact with the rollers.
The use of a turret or reel having three or more pairs of rollers to cradle the core and/or wound roll is well known. In some instances, as in U.S. Pat. No. 2,385,691, the core or roll being wound is entrapped between two cradle rolls and a third co-acting bedroll or between one of the turret rolls, a bedroll, and a third rider roll. The turret is indexed intermittently to move the core and product from a first winding station to a second station for completion of the wind. U.S. Pat. No. 2,984,426 describes a rotating turret with six rolls wherein the core and wound product are contained between two cradle rolls and a third co-acting bedroll or a pivoting rider roll.
A derivation of this approach according to U.S. Pat. No 4,327,877 involves the use of a drum instead of a turret. The roll being wound is trapped between the winding drum, a secondary winding drum mounted below the first winding drum, and a pivoting rider roll. In this instance, core advancement from a first winding stage to a second winding stage is achieved by introducing a speed differential between the two winding drums. The rider roll that pivots inwardly to create the three-roll entrapment must be pivoted out of the way for release of the wound log, and, for a discrete period of time, winding occurs without a positive three-roll entrapment. This results in the loss of positive continuous control for maintaining density and diameter control and creates the added disadvantage of a high inertia pivoting motion at higher log production rates, for example, about 15 or 20 per minute.
When a turret is used to support the cradle rolls, three-point entrapment is needed for the winding station. Intermittent indexing of the turret is speed limiting because of the high mass construction and inertia as the turret indexes. The machine must also compensate for the indexing advancement of the web in order to keep the web from breaking, especially at high indexing rates.
U.S. Pat. Nos. 4,327,877 and 4,133,495 utilize vacuum-providing for holding the web against the core. The vacuum acts on the web and does not assist in holding the core on the winding rolls.
The prior art also includes indexing reels having pairs of rider rolls therein working in conjunction with external devices to provide three-roll entrapment. These external devices take the form of pivot rolls, pivoting belt systems, and stationary belt systems as shown, for example, in U.S. Pat. Nos. 3,087,687 and 3,734,423. Again, intermittent motion of the turret is used to transfer the core and the small diameter wound roll to a second winding position where the roll is completed.